This invention relates to the art of catalytic cracking of hydrocarbons, and in particular to methods of inhibiting the deterioration of the zeolite catalysts due to contamination by metals, particularly vanadium, which are contained in the hydrocarbon feedstock. The problems associated with metal contamination of the catalyst during the catalytic cracking of hydrocarbons to yield light distillates such as gasoline as well as the actual conditions and procedures utilized are comprehensively documented in U.S. Pat. Nos. 4,101,417, 4,324,648, and 4,432,890, each of which is incorporated herein by reference. The invention herein represents an innovation and improvement over those processes set forth and claimed in U.S. Pat. Nos. 4,101,417 and 4,324,648.
More specifically, as described in U.S. Pat. No. 4,432,890 the carbon (coke) which deposits upon the zeolitic catalyst during the cracking process is eliminated by subjecting the catalyst upon removal from the catalytic cracking reactor to a regeneration stage. In this stage, the coked catalyst is heated with oxygen containing gas to a temperature of 1200.degree. F. where the coke is in essence converted and eliminated. Along with the deposition of coke on the catalyst is the deposition of metal contaminants (from feedstock) such as nickel, vanadium, iron and the like. Obviously, as the contamination level increases (both metal and coke), the effectiveness of the catalyst deteriorates.
While the regeneration process is quite effective in eliminating coke from the catalyst, the elevated temperature of regeneration is such as to cause a problem between the zeolite catalyst and any vanadium deposited therein. More specifically the vanadium is converted to vanadium oxides (pentoxide primarily) which possesses a melting point in the regeneration temperature range. Consequently the melting vanadium flows across the catalyst causing pore plugging, particulate coalescence, neutralization of the acidic groupings of the zeolite and generally causing irreversible damage to the crystalline structure of the zeolite.
The present invention is directed to a method of mitigating the destructive nature of the deposited vanadium on the zeolite catalysts.